DE102007022594A1 - Diagnostic method for a reagent to be introduced into an exhaust area of an internal combustion engine and apparatus for carrying out the method - Google Patents

Abstract

The invention relates to a diagnostic method for a reagent to be introduced into an exhaust gas region of an internal combustion engine, or a precursor of the reagent, which is required to convert at least one exhaust gas component in a catalytic converter, and to a device for performing the method. A change in the load of the internal combustion engine is first determined relative to time. If a load change threshold is exceeded, a first release signal is provided. The relative reagent material fill level in the catalytic converter is further determined. If a relative fill level threshold value is exceeded, a second release signal is provided. The reagent material slack occurring downstream of the catalytic converter is compared to a reagent material slack threshold value. If the first and second release signals are present and the reagent material slack threshold value is exceeded, the reagent material is considered to be of sufficient quality.

Description

State of the art

Disclosure of the invention

The The invention is based on a diagnostic method for a to be introduced into an exhaust region of an internal combustion engine reagent and a device for carrying out the method according to the preamble of the independent claims.

object The present invention also includes a controller program and a controller program product.

In the DE 199 03 439 A1 For example, a method and a device for operating an internal combustion engine are described, in the exhaust gas region of which an SCR catalytic converter (selective catalytic reduction) is arranged, which reduces the nitrogen oxides contained in the exhaust gas of the internal combustion engine to nitrogen with a reagent. The metering of the reagent preferably takes place as a function of operating parameters of the internal combustion engine, such as, for example, the rotational speed and the injected fuel quantity. Furthermore, the metering preferably takes place as a function of exhaust gas operating parameters, such as, for example, the exhaust gas temperature or the operating temperature of the SCR catalytic converter.

When Reagent is provided, for example, the reducing agent ammonia, which can be obtained from a urea-water solution. The Dosing of the reagent or starting materials of the reagent must be carefully determined. Too low dosage As a result, nitrogen oxides in the SCR catalyst are no longer complete can be reduced. Too high a dosage leads to a reagent slip, on the one hand to an unnecessary high reagent consumption and on the other hand, depending from the nature of the reagent, to an unpleasant one Odor nuisance may result. Still must It should be remembered that ammonia is toxic.

From the DE 10 2004 031 624 a method is described for operating an SCR catalytic converter used for cleaning the exhaust gas of an internal combustion engine, in which a control or regulation of the reagent filling level in the SCR catalytic converter is provided to a predetermined memory nominal value. On the one hand, the targeted specification of the desired storage value ensures that in transient states of the internal combustion engine a sufficient amount of reagent is available for eliminating the NOx emissions of the internal combustion engine as completely as possible and, on the other hand, that reagent slippage is avoided. The absolute reagent fill level of the SCR catalytic converter is determined on the basis of a catalyst model which takes into account the NOx mass flow flowing into the SCR catalytic converter, the NOx mass flow leaving the SCR catalytic converter, the catalyst temperature and, if appropriate, the reagent slip. The maximum possible reagent level of the SCR catalyst depends in particular on the operating temperature of the SCR catalyst. The maximum possible reagent level is highest at low operating temperatures and drops to lower values as the operating temperature increases. Instead of the absolute reagent level, therefore, the relative reagent level is considered, which is based on the possible under the given operating conditions of the catalyst maximum reagent level.

The Reduction of nitrogen oxides is only possible if the urea-water solution a given concentration or certain quality having. When filling the urea water solution tank with a lower quality urea-water solution or even with a wrong reagent or one In contrast, the precursor of a reagent is a reduction of the nitrogen oxides not ensured in the exhaust gas of the combustion unit.

In the DE 10 2006 055 235 A1 (not prepublished) is a diagnostic method for a urea-water solution is described in which during a predetermined period of time after filling the urea-water solution tank, the signal downstream of an SCR catalyst arranged exhaust gas sensor for determining the nitrogen oxide or Ammonia concentration is compared with predeterminable comparison values and is concluded in the case of deviation of the signal from the comparison values by specifiable threshold values to a lower quality urea-water solution.

Of the Invention is based on the object, a diagnostic method for a einzubringendes in an exhaust region of an internal combustion engine Reagent and a device for carrying out the Specify method that are easy to implement.

The The object is achieved by that in the independent claims specified features each solved.

Disclosure of the invention

The procedure according to the invention with the features of the independent method claim has the advantage that only the downstream of the catalyst, reagent slippage must be measured. The method steps can be carried out on the basis of existing variables known in a control unit, so that a minimum effort is required.

The inventive approach allows the recognition of the quality of the reagent used. By recognizing a bad quality or detecting a wrong reagent can be a warning. The carries the inventive approach therefore to ensure a consistently high conversion undesirable components of the exhaust gas of an internal combustion engine at.

advantageous Further developments and refinements of the invention Approach arise from dependent claims.

A Embodiment provides that in the presence of a first and second Release signal an averaging of the occurred and not Exceedances of a reagent-slip threshold is provided and that the reagent of sufficient quality is assigned when an average threshold is exceeded becomes. This increases the safety of the diagnosis and misdiagnoses due to sporadic events or interfering signals avoided.

The inventive device for implementation of the method initially relates to a control unit, the specially prepared means for carrying out the Has method. The control unit preferably contains at least one electrical memory, in which the method steps as Control unit program are stored.

The Controller contains a reagent level detection for determining the relative reagent fill level, a load change determination to determine a change the load of the internal combustion engine with respect to time and a Reagent Slip Comparator for Comparing Reagent Slip with a reagent slip threshold.

A Embodiment of the device according to the invention provides as exhaust gas sensor before a NOx sensor, which is a cross-sensitivity opposite to the reagent. Alternatively, as Exhaust gas sensor, a sensor whose sensitivity is specially designed with respect to the reagent. Provided provided as a reagent urea-water solution is, from which the reagent ammonia is recovered, can as Be provided exhaust gas sensor NH3 sensor.

The Control unit program according to the invention provides that all steps of the invention Procedure to be executed when it is in the control unit expires.

The Control unit program product according to the invention with a stored on a machine-readable carrier Program code carries the inventive Procedure when the program runs in the controller.

Further advantageous developments and refinements of the invention The procedure results from further dependent claims. Embodiments of the invention are in the drawing shown and in the following description in more detail explained.

It demonstrate:

1 a technical environment in which a method according to the invention runs and

2a - 2g Signal curves as a function of time.

1 shows an internal combustion engine 10 in the exhaust area 11 a reagent delivery device 12 , a catalyst 13 and an exhaust gas sensor are arranged. Upstream of the catalyst 13 occur NOx concentration% NOx_vK and downstream of the catalyst 13 a reagent slip% NH3_nK.

The reagent delivery device 12 is associated with a metering valve DV, which from a control unit 20 is applied with a dosing signal s_D. The exhaust gas sensor 14 puts the control unit 20 a reagent slip measurement signal NH3_Mes available.

The exhaust gas of the internal combustion engine 10 contains at least one undesired exhaust gas component, which is the catalyst 13 should diminish. Such an undesirable exhaust gas component is, for example, the NOx concentration% NOx_vK, which is in the catalyst 13 to be converted into less harmful compounds. It is assumed that the catalyst 13 needed for conversion, a reagent which is in the exhaust upstream of the catalyst 13 is introduced. The reagent can be introduced, for example, inside the engine. In the embodiment shown, it is assumed that the reagent via the reagent-introducing device 12 is metered into the exhaust gas. The amount of reagent is determined by the metering valve DV, which is acted upon by the dosing signal s_D. The dosing signal s_D puts the control unit 20 preferably based on known operating variables the internal combustion engine 10 such as the speed or load La fixed.

As a measure of the load La of the internal combustion engine 10 For example, the position of an accelerator pedal not shown in detail can be used, provided the internal combustion engine 10 is provided as a drive in a motor vehicle. As a measure of the load La can continue one of the internal combustion engine 10 be applied applied or provided torque. In addition, those of the internal combustion engine 10 supplied amount of air and / or an exhaust gas recirculation rate are taken into account.

In the exemplary embodiment shown, it is assumed that the catalyst 13 is configured as an SCR catalyst, which converts the NOx components of the exhaust gas with the reagent ammonia. The ammonia can, for example, from a urea-water solution as a precursor of the reagent by thermolysis in the exhaust gas region 11 obtained, wherein the urea-water solution via the reagent-introducing device 12 in the exhaust area 11 is sprayed.

To the Maintaining the highest possible conversion rate it requires that the reagent, in the illustrated embodiment the urea-water solution, a certain texture having. For example, in the case of a urea-water solution assumed a 32% urea-water solution. If the proportion of water either inadvertently or fraudulently Intention is increased, or if completely wrong Reagent used may have the desired conversion rate can no longer be achieved, so that legal requirements for emission control no longer be fulfilled.

The method according to the invention therefore sees a diagnosis of the exhaust gas area 11 the internal combustion engine 10 to be introduced reagent or a precursor of the reagent before. The diagnosis is based on that at a high reagent level in the catalyst 13 , which can store the reagent, and at a simultaneously occurring load step of the internal combustion engine 10 , which leads to an increase in the dosage of the reagent, a reagent slip% NH3_nK occurs from the exhaust gas sensor 14 detected and as a reagent slip measurement signal NH3_Mes the control unit 20 is made available. If such a reagent slip% NH3_nK can not be detected under the above conditions, and the components of the entire emission control system are otherwise in order, it can be assumed that a wrong or an insufficient reagent or a precursor of the reagent in the exhaust gas area 11 was introduced.

First, a load change of the internal combustion engine 10 detected. The temporal course of the load La is in 2a It is assumed that the diagnostic method starts at a first time ti1. A load change determination 30 the load La, the time ti and a load change threshold dLa / dt_Lim are provided. The load change determination 30 determines a temporal load change preferably based on the difference quotient of the load La. 2 B shows the load change signal dLa / dt as a function of the time ti. It is assumed that the load change signal dLa / dt exceeds the load change threshold dLa / dt_Lim at a third time ti3, so that at the third time ti3, a first enable signal FG1 from the load change determination 30 provided. The first enable signal FG1 can be generated from applicable maps of the input variables of the load change determination 30 be calculated.

It is assumed that with the occurrence of the first release signal FG1 a corresponding increase in the dosage of the reagent takes place, with respect to the storage capacity of the catalyst 13 an overdose of the reagent can occur with respect to the reagent, resulting in an increased reagent slip% NH3_nK. However, a large increase in reagent slip% NH3_nK only occurs when the storage capacity of the catalyst 13 is largely exhausted before increasing the dosage.

It is therefore still contemplated, the relative reagent level% FS in the catalyst 13 in a reagent level detection 32 to determine what the NOx concentration% NOx_vK, the temperature te_Kat of the catalyst 13 as well as the dosing signal s_D be made available. The determination of the relative reagent fill% FS can the above-mentioned prior art according to DE 10 2004 031 624 A1 to be taken in detail, to which express reference is made.

Determining the relative reagent level% FS instead of the absolute reagent level is particularly useful because the reagent storage capability of an SCR catalyst 13 strongly depends on the temperature, wherein a certain absolute reagent level at a low catalyst temperature te_Kat a comparatively low relative reagent level% FS and at a high catalyst temperature te_Kat a comparatively high relative reagent level% FS corresponds. In 2d is a possible course of the relative reagent level% FS shown, with a relative level threshold% FS_Lim is entered, which is exceeded at a second time ti2. In a level comparator 34 the relative reagent level% FS is compared with the relative level threshold% FS_Lim. The level comparator 34 provides a second enable signal FG2 when the relative reagent level% FS exceeds the relative level threshold% FS_Lim. The second enable signal FG2 can be applied from maps of the input variables of the level comparator 34 be calculated. For example, the relative level threshold% FS_Lim is set to at least 70 percent. Exceeding the relative level threshold% FS_Lim occurs according to 2d at the second time ti2 and performs according to 2e for providing the second enable signal FG2.

The envisaged detection and evaluation of the reagent slip% NH3_nK is based on the fact that in the case of the present first and second release signal FG1, FG2 an overdose of the reagent is assumed. A reagent slip comparator 36 compares the reagent slip measurement signal NH3_Mes with a reagent-slip threshold NH3_Lim, wherein the reagent-slip comparator 36 provides a first evaluation signal B1 when the reagent slip measurement signal NH3_Mes exceeds the reagent-slip threshold NH3_Lim. The reagent slip measurement signal NH3_Mes including the reagent slip threshold NH3_Lim are in 2f shown, wherein the exceeding of the reagent slip threshold NH3_Lim occurs at a fourth time ti4. The excess leads according to 2g at the fourth time ti4 for providing the first evaluation signal B1.

Due to the dynamic processes in the catalyst 13 as well as due to the duration of the exhaust gas in the exhaust gas area 11 Preferably, a small delay time ti_V is scheduled between the third and fourth times ti3, ti4. The delay time ti_V becomes the reagent slip comparator 36 made available.

The Occurrence of the first evaluation signal B1 means that an expected Reaction occurred, so that it can be assumed that the reagent had a given quality Has. If, despite the presence of the two enable signals FG1, FG2 no first evaluation signal B1 occurs, it must be assumed that the reagent or the precursor of the reagent no has sufficient quality or even a wrong one Reagent was used.

In order to increase the reliability of the diagnostic method according to the invention, according to an embodiment it can be provided that not every occurrence of the first evaluation signal B1 or a corresponding absence of the first evaluation signal B1 is used for immediate statement as to whether a sufficient quality of the reagent is present or not. Therefore, an average comparator is provided 38 to which the first evaluation signal B1, the first and second enable signals FG1, FG2, and a mean threshold BM_Lim are provided. The mean value comparator 38 provides a second evaluation signal B2 when an average of the occurrence or non-occurrence of the first evaluation signal B1 exceeds the average threshold BM_Lim. When the second evaluation signal B2 occurs, it is assumed that the quality of the reagent has been sufficient.

According to another embodiment, it is provided that the reagent threshold value NH3_Lim of the load La of the internal combustion engine 10 and / or the relative reagent level% FS depends. A reagent slip threshold setting 40 Contains characteristic curves, for example, which determine the relationship.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 19903439 A1 [0003]
• - DE 102004031624 [0005]
• DE 102006055235 A1 [0007]
• - DE 102004031624 A1 [0032]

Claims (10)

Diagnostic method for an exhaust area ( 11 ) an internal combustion engine ( 10 ) to be introduced reagent or a precursor of the reagent, which for the conversion of at least one exhaust gas component in a catalyst ( 13 ) is required, characterized in that a change in the load (La) of the internal combustion engine ( 10 ) is determined based on the time (ti) and when a load change threshold value (dLa / dt_Lim) is exceeded, a first enable signal (FG1) is provided that the relative reagent fill level (% FS) in the catalyst ( 14 ) and when a relative level threshold (% FS_Lim) is exceeded, a second enable signal (FG2) is provided which is downstream of the catalyst ( 13 reagent slippage (% NH3_nK) is compared with a reagent slip threshold (NH3_Lim) and that, when the first and second release signals (FG1, FG2) are present, sufficient quality is assigned to the reagent when the measured reagent slippage (% NH3_nK) exceeds the reagent slippage. Threshold (NH3_Lim) exceeds. Method according to claim 1, characterized in that in the presence of the first and second enable signal (FG1, FG2) an averaging of the occurred and the not occurred exceedances of the reagent slip threshold (NH3_Lim) and that the reagent is assigned a sufficient quality when the mean exceeds an average threshold (BM_Lim). Method according to claim 1 or 2, characterized that after the last released enable signal (FG1, FG2) a Delay time (ti_V) is waited before the reagent slip (% NH3_nK) with the reagent slip threshold (NH3_Lim) is compared. Diagnostic device for an exhaust area ( 11 ) an internal combustion engine ( 10 ) to be introduced reagent or a precursor of the reagent, which for the conversion of at least one exhaust gas component in a catalyst ( 13 ) is required, characterized in that a control unit ( 20 ) with means ( 30 . 32 . 34 . 36 ) is provided for carrying out the method according to one of the preceding claims. Diagnostic device according to claim 4, characterized in that the control device ( 20 ) a load change determination ( 30 ) for determining a change in the load (La) of the internal combustion engine ( 10 ) with respect to time (ti), a reagent level detection ( 32 ) to determine the relative reagent level (% FS), a level comparator ( 34 ) for comparing the relative reagent level (% FS) in the catalyst ( 13 ) with a relative fill level threshold (% FS_Lim) and a reagent-slip comparator ( 36 ) for comparing a reagent slip (NH3_Mes) with the reagent slip threshold (NH3_Lim). Diagnostic device according to claim 4, characterized in that as exhaust gas sensor ( 14 ) a NOx sensor is provided which has a cross-sensitivity to the reagent. Diagnostic device according to claim 4, characterized in that as exhaust gas sensor ( 14 ) an NH3 sensor is provided. Diagnostic device according to claim 4, characterized in that that provided as a reagent urea-water solution is. Control unit program that performs all the steps of a method according to one of claims 1 to 3, when the program is stored in a control unit ( 20 ) expires. A control program product having a program code stored on a machine-readable carrier for carrying out the method according to one of claims 1 to 3, when the program is stored in a control device ( 20 ) is performed.